Biomechanical studies of the rabbit patellar tendon after removal of its one-fourth or a half

Preoperative magnetic resonance assessment of patellar tendon dimensions for graft selection in anterior cruciate ligament reconstruction

BACKGROUND

A bone patellar tendon bone autograft is one of the standard graft choices for anterior cruciate ligament reconstruction. However, its use can be limited when the patellar tendon is too narrow or too long.

HYPOTHESIS

A preoperative assessment of patellar tendon dimensions using magnetic resonance imaging would be accurate and reliable. Patients undergoing anterior cruciate ligament reconstruction would have wide ranges of patellar tendon dimensions, and a significant proportion of patients would have a too narrow and/or too long patellar tendon as the graft choice. There would be a demographic predictor to identify the patients with inappropriate patellar tendon dimensions.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 3.

METHODS

The accuracy and reliability of magnetic resonance assessments of patellar tendon dimensions were assessed by comparing the intraoperative measurements using a ruler in 55 knees and 10 knees, respectively. Data from the magnetic resonance assessments in 147 knees undergoing anterior cruciate ligament reconstruction were used for the normative documentation of the patellar tendon dimensions (width, thickness, and length) and identification of demographic predictors for the dimensions.

RESULTS

Preoperative magnetic resonance assessments of the patellar tendon dimensions were accurate and reliable. Korean patients undergoing anterior cruciate ligament reconstruction had wide variations in patellar dimensions, and a significant portion of the patients had an inappropriate patellar tendon (longer than 5 cm in 4.1% and narrower than 27 mm at middle portion in 15.6%) for the graft source. Patient height was the predictor used for patellar tendon width. The mathematical equation used to estimate the width based on patient height was: tendon width at middle portion (mm) = 0.202 x patient height (cm) - 5.07.

CONCLUSION

Preoperative magnetic resonance assessment of patellar tendon dimensions can be a valuable tool with satisfactory accuracy and reliability when the autologous patellar tendon is considered as the graft source for anterior cruciate ligament reconstruction.

The role of repair tension on tendon to bone healing in an animal model of chronic rotator cuff tears

Rotator cuff tendon tears are one of the most common shoulder injuries. Although surgical repair is typically beneficial, re-tearing of the tendons frequently occurs. It is generally accepted that healing is worse for chronic tears than acute tears, but the reasons for this are unknown. One potential cause may be the large tensions that are sometimes required to repair chronically torn tendons back to bone (i.e., repair tension). Therefore, the objective of this study was to utilize an animal model of chronic rotator cuff repairs to investigate the role of increased repair tension on tendon to bone healing. We hypothesized that an increase in repair tension would be related to detrimental changes to the healing insertion site. To test this hypothesis, the supraspinatus tendon of rats was surgically detached and then repaired immediately or after a delay of 2, 4, or 16 weeks. The repair tension was measured using a tensiometer and the mechanical properties, collagen organization, and protein expression of the healing insertion site were evaluated 4 and/or 16 weeks following repair. We found that the repair tension increased with time following detachment, and was related to a decrease in the failure properties and viscoelastic peak stress and an increase in cross-sectional area and stiffness of the insertion site. Therefore, repair tension should be minimized in the clinical setting. Future studies will include additional animal model studies involving the relationship between tension and muscle properties and a clinical study investigating the role of repair tension on repair failure.

The effect of transforming growth factor-beta on mechanical properties of the fibrous tissue regenerated in the patellar tendon after resecting the central portion

BACKGROUND

No investigators have studied the effects of an application of growth factors on the in vivo tissue regeneration in the tendon after resecting the central portion. The purpose of this study is to clarify whether an application of transforming growth factor (TGF)-beta1 increases the mechanical properties of the regenerated tissue in the patellar tendon after resecting the central portion.

METHODS

Thirty female rabbits were divided into three groups, after a 3 mm wide and 10 mm long tendon substance was resected from the central portion in the patellar tendon. In Group I, 5-ng TGF-beta1 dissolved in 0.1-ml saline was injected into the resected portion in the patellar tendon. In Group II, only 0.1-ml saline was injected into the resected portion. In Group III, nothing was injected. All animals were sacrificed at 6 weeks after surgery. Mechanical and histological evaluations were made concerning the regenerated tissue and the unresected tendon tissue in the patellar tendon.

FINDINGS

Concerning the regenerated tissue, the tangent modulus and the tensile strength of Group I were significantly greater than those of Groups II and III, while there were no significant differences in these parameters between Groups II and III.

INTERPRETATION

The application of TGF-beta1 significantly increases the tangent modulus and the tensile strength of the fibrous tissue regenerated in the patellar tendon after resecting the central portion. This study has provided basic important information on the utility of TGF-beta1 in the in vivo tendon regeneration.

Effects of the Frequency and Duration of Cyclic Stress on the Mechanical Properties of Cultured Collagen Fascicles From the Rabbit Patellar Tendon

The effects of frequency or duration of cyclic stress on the mechanical properties of collagen fascicles were studied by means of in vitro tissue culture experiments. Collagen fascicles of approximately 300μm in diameter were obtained from rabbit patellar tendons. During culture, cyclic stress having the peak stress of approximately 2MPa was applied to the fascicles at 1Hz for 1hour∕day (1Hz-1h group), at 1Hz for 4hours∕day (1Hz-4h group), or at 4Hz for 1hour∕day (4Hz-1h group). The frequency of 4Hz and the duration of 1hour∕day are considered to be similar to those of the in vivo stress applied to fascicles in the intact rabbit patellar tendon. After culture for 1 or 2weeks, the mechanical properties of the fascicles were determined using a micro-tensile tester, and were compared to the properties of non-cultured, fresh fascicles (control group) and the fascicles cultured under no load condition (non-loaded group). The tangent modulus and tensile strength of fascicles in the 4Hz-1h group were similar to those in the control group; however, the fascicles of the 1Hz-1h and 1Hz-4h groups had significantly lower values than those of the control group. There was no significant difference in the tensile strength between the 1Hz-1h and non-loaded groups, although the strength in the 1Hz-4h group was significantly higher than that of the non-loaded group. It was concluded that the frequency and duration of cyclic stress significantly affect the mechanical properties of cultured collagen fascicles. If we apply cyclic stress having the frequency and duration which are experienced in vivo, the biomechanical properties are maintained at control, normal level. Lower frequencies or less cycles of applied force induce adverse effects.

Primary repair of posterior cruciate ligament avulsion fracture: the effect of occult injury in the midsubstance on postoperative instability

BACKGROUND

In the posterior cruciate ligament avulsion fracture, posterior instability cannot be completely restored by the anatomical reduction and fixation of an avulsed fragment.

HYPOTHESIS

The occult midsubstance injury inside the posterior cruciate ligament may affect the residual posterior instability after anatomical reduction and internal fixation of the avulsed fragment.

STUDY DESIGN

Prospective comparative clinical study.

METHODS

Thirty-one patients were followed for a period of 2 to 8 years. Based on magnetic resonance images taken immediately after the injury, these patients were divided into 2 groups, the occult injury group (group O, 15 knees) and the uninjured group (group N, 16 knees).

RESULTS

The side-to-side difference of the posterior knee instability was 3.2 mm in group O and 3.0 mm in group N. Approximately 60% of the knees examined showed mild posterior instability in both groups. There were no significant differences found between the 2 groups.

CONCLUSION

The occult posterior cruciate ligament midsubstance injury does not significantly affect postoperative posterior instability of the knee. This fact did not support the hypothesis that has been commonly considered thus far.

CLINICAL RELEVANCE

It is not necessary for orthopaedic surgeons to be overly apprehensive about occult midsubstance injury in the treatment of posterior cruciate ligament avulsion fracture.

Effects of Cyclic Stress on the Mechanical Properties of Cultured Collagen Fascicles from the Rabbit Patellar Tendon

Effects of cyclic stress on the mechanical properties of collagen fascicles were studied by in vitro tissue culture experiments. Collagen fascicles (approximately 300 μm in diameter) obtained from the rabbit patellar tendon were applied cyclic load at 4 Hz for one hour per day during culture period for one or two weeks, and then their mechanical properties were determined using a micro-tensile tester. There was a statistically significant correlation between tensile strength and applied peak stress in the range of 0 to 5 MPa, and the relation was expressed by a quadratic function. The maximum strength (19.4 MPa) was obtained at the applied peak stress of 1.8 MPa. The tensile strength of fascicles were within a range of control values, if they were cultured under peak stresses between 1.1 and 2.6 MPa. Similar results were also observed in the tangent modulus, which was maintained at control level under applied peak stresses between 0.9 and 2.8 MPa. The stress of 0.9 to 1.1 MPa is equivalent to approximately 40% of the in vivo peak stress which is developed in the intact rabbit patellar tendon by running, whereas that of 2.6 to 2.8 MPa corresponds to approximately 120% of the in vivo peak stress. Therefore, the fascicles cultured under applied peak stresses of lower than 40% and higher than 120% of the in vivo peak stress do not keep the original strength and modulus. These results indicate that the mechanical properties of cultured collagen fascicles strongly depend upon the magnitude of the stress applied during culture, which are similar to our previous results observed in stress-shielded and overstressed patellar tendons in vivo.

The changes in mechanical properties of regenerated and residual tissues in the patellar tendon after removal of its central portion

OBJECTIVE

To know the temporal changes of the mechanical properties of the regenerated and the residual tissues in the patellar tendon after removal of the central portion.Design. The regenerated and the residual tissues were compared to sham-operated tendons.

BACKGROUND

Although the structural properties of the whole patellar tendon after removal of the central portion have been investigated, no studies have distinguished between the regenerated and the residual tissues.Methods. For 52 skeletally mature rabbits, a full-thick, segmental defect was made at the central portion of the right patellar tendon, while a sham operation performed in the left tendon. At 3, 6, 12, and 24 weeks, we evaluated the mechanical properties and fibroblast density of the regenerated and the residual tissues as well as the blood flow and tissue dimensions of the patellar tendon. In addition, non-treated patellar tendons from six rabbits were served as the control for mechanical testing.

RESULTS

The tangent modulus and the tensile strength of the regenerated tissue progressively increased with time. On the other hand, these parameters of the residual tendinous portion decreased until 6 weeks, although they gradually increased thereafter. The tensile strength of the regenerated and the residual tissues at 24 weeks were approximately 80% and 75%, respectively, of the non-treated, control tendon. Abundant blood flow and cell proliferation were observed in the regenerative tissue until 6 weeks.

CONCLUSION

The mechanical properties of the regenerated and the residual tissues after removal of the central portion in the patellar tendon are much different from those of the original tendon.

RELEVANCE

The present study showed inferior mechanical properties of the residual and the regenerated tissues for up to 24 weeks after removal of the central portion in the patellar tendon. Therefore, the aggressive rehabilitation that applies excessive load to the patellar tendon should be avoided at an early stage after harvesting the tendon for ligament reconstruction.

Effects of static stress on the mechanical properties of cultured collagen fascicles from the rabbit patellar tendon

In-vitro tissue culture experiments were performed to study the effects of static stress on the mechanical properties of collagen fascicles obtained from the rabbit patellar tendon. After collagen fascicles having the diameter of approximately 300 microm were cultured for 1 and 2 wk under static stress between 0 and 3 MPa, their mechanical properties and crimp morphology were determined using a micro-tensile tester and a light microscope, respectively. The tensile strength and tangent modulus of the fascicles were significantly decreased by culture under no load compared to control fascicles. A statistically significant correlation, which was described by a quadratic curve, was observed between applied stress and tensile strength. The maximum tensile strength (16.7 MPa) was obtained at the applied stress of 1.2 MPa; the strength was within a range of control values. There was a similar correlation between applied stress and tangent modulus, and the modulus was maintained at control level under 1.3 MPa stress. The stress of 1.2 to 1.3 MPa is equivalent to approximately 50 percent of the peak stress developed in the intact rabbit patellar tendon by running. Strain at failure of cultured collagen fascicles was negatively correlated with applied stress, and that at 1.2 to 1.3 MPa stress was almost the same as the control value. Crimp morphology in the fascicles cultured under about 1.2 MPa stress was similar to that in control fascicles. These results indicate that cultured collagen fascicles change the mechanical properties and structure in response to static tensile stress. In addition, their mechanical properties and structure are maintained at control level if the static stress of 50 percent of in-vivo peak stress is applied.

Effects of stress shielding on the transverse mechanical properties of rabbit patellar tendons

With the aim of studying mechanisms of the remodeling of tendons and ligaments, the effects of stress shielding on the rabbit patellar tendon were studied by performing tensile and stress relaxation tests in the transverse direction. The tangent modulus, tensile strength, and strain at failure of non-treated, control patellar tendons in the transverse direction were 1272 kPa, 370 kPa, and 40.5 percent, respectively, whereas those of the tendons stress-shielded for 1 week were 299 kPa, 108 kPa, and 40.4 percent, respectively. Stress shielding markedly decreased tangent modulus and tensile strength in the transverse direction, and the decreases were larger than those in the longitudinal direction, which were determined in our previous study. For example, tensile strength in the transverse and longitudinal direction decreased to 29 and 50 percent of each control value, respectively, after 1 week stress shielding. In addition, the stress relaxation in the transverse direction of stress-shielded patellar tendons was much larger than that of nontreated, control ones. In contrast to longitudinal tensile tests for the behavior of collagen, transverse tests reflect the contributions of ground substances such as proteoglycans and mechanical interactions between collagen fibers. Ground substances provide lubrication and spacing between fibers, and also confer viscoelastic properties. Therefore, the results obtained from the present study suggest that ground substance matrix, and interfiber and fiber-matrix interactions have important roles in the remodeling response of tendons to stress.